Angelopoulos et al., U.S. Pat. No. 6,025,057 discloses a solution to a problem of making electronic packages, for example printed circuit boards, in which a key requirement for making the same is the achievement of an appropriate Pd/Sn seed layer catalyst loading. Insufficient Pd catalyst will lead to voids in a copper deposited circuit layer creating open circuits. Too much catalyst can cause both adhesive failure and lateral conduction. Adhesive failure permits electroless plating solution to leak beneath the photoresist and deposit copper between circuit elements causing short circuits. The disclosed solution to the problem involves depositing an organic polyelectrolyte onto an organic substrate, such as a circuit board formed from fiberglass and epoxy. A colloidal palladium-tin seed layer is deposited on top of the organic polyelectrolyte. This is followed by depositing a photoimageable polymer on top of the seed layer, and photolithographically patterning the photoimageable polymer to uncover portions of the seed layer. Electroless deposition of copper is used to deposit copper over the uncovered portions of the seed layer. The organic polyelectrolyte is deposited from an aqueous solution at a pH appropriate for the desired seed catalyst coating. A disclosed example of an organic polyelectrolyte is a copolymer of acrylamide and beta-metacryloxy ethyl trimethyl ammonium methylsulfate. The above polyelectrolyte includes hydrolyzed amide groups and is deposited on the organic substrate in an aqueous solution containing sulfuric acid at a pH below 4. In another embodiment the polyelectrolyte is deposited on the organic substrate in an aqueous solution containing sodium hydroxide at a pH above 10. Another polyelectrolyte disclosed is a cationic polyamide-amine. A neutral aqueous solution is deployed with the polyelectrolyte concentration ranging between 0.2 and 1.2 grams per liter. A seed layer of Pd/Sn colloidal suspension is deposited over the polyelectrolyte.
Angelopoulos et al., U.S. Pat. No. 5,997,997 issued Dec. 7, 1999, discloses a solution to a problem associated with fabricating circuitized structures, such as printed circuit boards, wherein conventional electroless plating methods often suffer from excessive seed deposition. The presence of excessive seed on the circuit board leads to leakage shorts, poor adhesion of the photoresist used to circuitize the circuit board on the seed layer due to uneven surfaces. The excess seed layer can also lead to unwanted metal plating in subsequent processing steps. The disclosed solution includes providing a work piece including a substrate coated with a polymeric dielectric layer. The work piece with the polymeric dielectric layer is then baked in the surrounding ambient atmosphere. Thereafter, the work piece is treated with a polymeric surfactant which is capable of hydrogen bonding to weak acid groups on the surface of the polymeric dielectric. A disclosed polymeric surfactant is a cationic polyelectrolyte, having amide groups, such as cationic polyacrylamide or cationic polyamido-amine. The polymeric surfactant has a molecular weight ranging from 105 to 107. A disclosed polyelectrolyte is available under the trade name “Polytech” from Polytech, Inc.
In a field unrelated to printed circuit boards, the fabrication of fuel cell stacks includes the making of bipolar plates with water management features. Capillary driven instability of liquid films in hydrophobic bipolar plate channels can result in liquid holdup and loss of fuel cell performance. Plasma processing to introduce hydrophilic functional groups on the surface of bipolar plates has been shown to eliminate liquid holdup and improve fuel cell performance. However, such plasma processing techniques are very expensive and time consuming. Hence, alternative processing options are needed. One such option is disclosed in assignee's provisional U.S. Patent Application No. 60/707,705, entitled “Fuel Cell Component With Coating Including Nanoparticles.” This approach involves spraying a thin coating of hydrophilic nanoparticles onto the bipolar plate surface. However, Applicants have discovered a number of durability concerns may exist with such a process including: (1) the lack of color reflectivity from the coating suggests coverage by the coating is not coherent, (2) that organic acid and surfactant residues remain with the coating, and (3) the strength of the coating is a result of cohesive rather than adhesive interactions (that is, little or no chemical bonding of the coating to the substrate). The present invention provides alternatives to the prior art.